Antenna Tuning or Cutting

Antenna Tuning or Cutting


Selecting and installing a proper antenna for a telemetry radio, GPS transponder, or base station involves selecting a suitable style of antenna for your installation, properly mounting the antenna, cabling the antenna to the radio connection, and possibly adding a lightning arrestor to the antenna cable.  One of the most important considerations is ensuring you select an antenna that works well for your operating frequency.  In many cases this involves tuning the antenna for the proper frequency.

Any antenna is constructed of a metal conducting element.  Often this element is insulated from direct contact with a rubber or fiberglass sheath, or some other material and you will not see the metal element itself.   In any good antenna the shape and length of the element was carefully considered when the antenna was designed.  Some elements are simple straight thin metal rods, others are coils, loops or other styles or combinations.  Frequently the antenna is built to work at a very specific frequency or range of frequencies, such as 450-460MHz.  If you select an antenna built for the wrong frequency you will have very poor results.

Some common antennas allow for the user to adjust the antenna for their frequency.  The antenna may be built to cover a wide range of frequencies, such as 400-500MHz, but should be adjusted to the precise user frequency.  As radio transmissions are actually radio “waves” you may remember that a radio frequency and radio wavelength are tightly related.  Tuning an antenna typically involves adjusting the length of the conducting element(s) to be a specific ratio of the actual radio wavelength.

Often field tunable antennas involve 2 elements that are allowed to slide or telescope back and forth to achieve a specific antenna length.  In other cases the element(s) may need to be physically cut or altered to a specific length.   In the case of a common omni-directional fiberglass antenna the metal element(s) are housed within a fiberglass insulative sheath, and must be removed from the sheath to gain access.  Here the user must expose the metal conductive element(s) and cut them to the proper length.  If the antenna has multiple elements , each element may require a different cut and re-assembly must place them in proper order.

To physically cut the element(s) a good metal file, Dremel tool, or fine tooth metal saw may be used to cut the element(s), or score and snap them carefully.  Once done the element(s) go back into the fiberglass sheath in correct order.  You can smooth any sharp points first if you like.

 If an antenna is meant to be tunable it will come with a chart or other instructions as to what length is intended for a specific frequency, and perhaps instructions on how to physically perform the cut or adjustment.  If  you intend to cut-to-tune your antenna remember these 5 key points:

  • Never cut an antenna unless you are certain you need to do so.
  • Make sure you have clear instructions on how to measure and cut the antenna for your frequency, and measure very carefully.
  • If the antenna contains multiple elements, plan and track each element with individual care.
  • Wear eye protection and follow any safety procedures.
  • Never cut the element too short.  It may be better to take it increments at a time to achieve proper length.

If you order an antenna from us that requires cutting, we are happy to do this for you prior to shipping if you can tell us the precise frequency you need.